RU2708319C2 - Medical system - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention refers to medical equipment, namely to a medical system for penetration into an anatomical structure of a patient, which contains tissues with different abilities to conduct electric current. System comprises housing, first and second electrodes, electric generator and processing device. Body is configured to penetrate the anatomical structure and has an outer surface. First electrode comprises a first contact surface on the external surface of the body for contact with tissues of the anatomical structure. Second electrode comprises a second contact surface on the outer surface of the body to come into contact with tissues of the anatomical structure at a distance from the first contact surface. Electric generator is configured to supply electric current between first and second contact surfaces. Processing device is configured to determine an electrical characteristic which reflects the ability of the anatomical structure tissue between the first and second contact surfaces to conduct electric current and to output a warning signal corresponding to a certain electrical characteristic. Parameter of warning signal varies depending on certain electric characteristic. Warning signal is intermittent and has a warning rate where warning sections are sent in series with a time interval between two consecutive warning sections. Processing device is configured to detect a change in the electrical characteristic and to vary said parameter after the delay time elapsing following the change in the electrical characteristic.

EFFECT: higher reliability of medical system and reduced risk of distortions due to reduction of untimely changes of warning signal by delay time and transmission of warning signal with delay to limit or modulate sensitivity of medical system to point changes of measured parameters.

13 cl, 7 dwg

Description

The invention relates to a medical system.

In particular, the invention relates to a medical system for penetrating into the anatomical structure of a patient, said anatomical structure containing tissues having different abilities to conduct electric current. The medical system contains:

- a housing configured to penetrate the anatomical structure, the housing having an outer surface,

- at least one first electrode containing a first contact surface located on the outer surface of the housing, to come into contact with tissues of the anatomical structure,

- at least one second electrode containing a second contact surface located on the outer surface of the housing, to come into contact with tissues of the anatomical structure at a distance from the first contact surface,

- an electric generator configured to supply electric current between the first and second contact surfaces,

- a processing device configured to determine an electrical characteristic that displays the ability of the tissue of the anatomical structure to conduct electric current between the first and second contact surfaces, and with the ability to issue a warning signal corresponding to a specific electrical characteristic, while the warning signal has at least one parameter that varies depending on a specific electrical characteristic.

Patent application WO 03/068076 describes a medical system of the aforementioned type in the form of a surgical instrument, in which the warning signal is intermittent and has a warning pace at which the warning portions received by the user are transmitted sequentially with the time interval between two successive warning portions.

This surgical instrument, marketed under the name PediGuard®, is used, in particular, in orthopedic surgery to ensure proper positioning of the pedicular screws in the leg of the patient’s vertebra to secure the prosthesis or implant. Indeed, it is very important to ensure accurate positioning of the pedicular screws in the cancellous bone of the vertebral legs in order to properly secure the prosthesis or implant, while avoiding damage or breakdown of the inner layer of the cortical bone, which limits the vertebral foramen in which the spinal cord passes, or the outer layer of the cortical bone, near which are the roots of nerves. Changes in the warning signal provide information about the tissues near the first and second contact surfaces, while the cortical bone has less electrical conductivity than the spongy bone, which in turn has less electrical conductivity than fluids such as blood or soft tissues.

The surgical instrument is simple and intuitive to use and provides indicative success rates when installing pedicular screws.

At the same time, in some specific situations, in particular, when the tissues encountered have numerous local heterogeneities, the sensitivity of a surgical instrument to purely point changes in its ability to conduct electric current can lead to some difficulties in interpreting the warning signal. In particular, these point changes can be expressed by untimely changes in the warning signal, interrupting the expected sequence of warning sections and time intervals. Changes in the ability to conduct electric current that occur many times over a short period of time can also lead to distortions in the warning signal, which give the doctor incomprehensible or difficult to interpret information.

In these particular situations, the normal use of a surgical instrument may be based on the experience of the physician, allowing him to highlight the information that he must consider.

The invention is intended to solve this problem by increasing the reliability of the medical system, regardless of its use.

In connection with this invention, there is provided a medical system of the aforementioned type in which the processing device is configured to detect a change in the electrical characteristic and change the at least one variable parameter of the warning signal after the delay time following the change in the electrical characteristic has elapsed.

Thus, according to the invention, the period determined by the delay time precedes the transmission of an alarm with a parameter or parameters corresponding to a specific electrical characteristic. Thus, a warning signal with a parameter or parameters corresponding to a specific electrical characteristic is transmitted with a delay with respect to detecting a change in the electrical characteristic. The delay time allows you to limit or modulate the sensitivity of the medical system to point changes in the ability of the tissues to conduct electrical current. Due to this, untimely changes in the warning signal are reduced, the risks of occurrence of distortions are reduced, and the reliability of the medical system is increased.

The delay time may be equal to at least a portion of the warning period corresponding to the pace of the warning, in particular equal to at least a portion of the time interval, preferably from 30% to 100% of the time interval, in particular from 50% to 100%, for example from 60% up to 90%.

According to an alternative embodiment, the processing device can determine the electrical characteristic with a measurement frequency, wherein the electric current has a measurement period corresponding to the measurement frequency, wherein the delay time can be at least a portion of the measurement period, preferably 10% to 500% of the measurement period.

The delay time can be twice the measurement period, and the processing device can be configured to calculate the average electrical characteristic based on the electrical characteristics determined in each of the measurement periods occurring during the delay time, and with the possibility of changing the parameter of the warning signal depending on calculated average electrical characteristics.

The measurement period may be from 50 ms to 250 ms, preferably 200 ms.

The specified at least one variable parameter of the alarm signal may include a warning rate, while the processing device is configured to change the warning rate after the expiration of the delay time.

The warning rate can range from 1 Hz to 20 Hz.

The specified at least one variable parameter of the warning signal may include a warning frequency at which each of the warning sections is transmitted, and the processing device is configured to change the warning frequency after the delay time has elapsed.

The warning frequency can range from 470 Hz to 2600 Hz.

The specified at least one variable parameter of the warning signal may include the amplitude of the warning, while the processing device is configured to change the amplitude of the warning after the expiration of the delay time.

The processing device may be configured to determine electrical conductivity as an electrical characteristic and with the ability to:

- increase the parameter of the warning signal when the conductivity increases,

- reduce the alarm parameter when the conductivity decreases.

Alternatively, the processing device may be configured to determine resistivity as an electrical characteristic and with the ability to:

- increase the parameter of the warning signal when the resistivity decreases,

- decrease the alarm parameter when the resistivity increases.

The processing device may be configured to keep at least one variable alarm parameter constant while the electrical characteristic remains below a threshold and to change a warning parameter when the electrical characteristic reaches a threshold.

Other objects and advantages of the invention will be more apparent from the following description of a particular embodiment of the invention, presented by way of non-limiting example with reference to the accompanying drawings.

In FIG. 1 shows a schematic view of a medical system according to an embodiment of the invention, wherein the medical system comprises a processing device configured to give an alert signal corresponding to an electrical characteristic that displays the ability of tissue of an anatomical structure to conduct electrical current between the first and second contact surfaces;

in FIG. 2 is an image of an intermittent warning signal having a warning rate at which warning portions sensed by a user are transmitted sequentially with a time interval between two successive warning portions, with each warning port having a warning frequency and a warning amplitude;

in FIG. 3 - image of the measurement signal (M) and three warning signals (A, B, C), transmitted respectively during the penetration of the medical system into three different anatomical structures, while the warning rate, warning frequency and warning amplitude change after the delay time has elapsed, depending from changes in electrical characteristics;

in FIG. 4 is an image of a transition function recorded in the processing device and relating the value of the warning rate, warning frequency and / or amplitude of the warning to each of the values of the electrical characteristic;

in FIG. 5, 6 and 7 are images of the measurement signal and the warning signal during the penetration of the medical system into the vertebrae of the patient’s spine.

In the figures, identical or similar elements have the same designations.

In FIG. 1 schematically shows a medical system in the form of a surgical instrument 10 manually manipulated by a physician to drill a bone structure 3, such as a vertebra 2 of a patient's spine. However, the invention is not limited to this type of surgical instrument and use for bone structure. In particular, the invention can be applied to any type of anatomical structure with any type of medical system, manually manipulated or using a robotic arm. The medical system may comprise any type of surgical or medical instrument, manual or mechanized, and in particular a probe, square tip, drill, spatula or curette. It may also contain an implant, such as a screw, in particular a pedicular screw.

The tool 10 comprises a housing 11 configured to penetrate the bone structure 3, and a housing 20 forming a handle connected to the housing 11 and configured to be held in the doctor’s hand. Depending on the application, the casing 20 may also be configured to connect to the end of the robotic arm.

The casing 11 has an outer surface 12, which serves as a holder for the first 16 and second 17 electrodes, respectively having first 16 a and second 17 a contact surfaces configured to come into contact with the bone structure 3 at a distance from each other.

In the presented embodiment, the housing 11 is conical with a circular cross section around the central axis D and extends from the proximal end 13, which is connected, possibly detachably, to the handle 20, to the distal end 14 forming a penetrating end in the form of a truncated cone or pyramid. However, the housing 11 may have any other shape, in particular conical or cylindrical with a polygonal or other cross-section.

The first electrode 16, having a cylindrical shape and made of conductive material, extends inside the housing 11 parallel to the central axis D. In particular, the first electrode 16 is located in the central hole of the housing 11 and extends coaxially with the central axis D to the free end forming the first contact surface 16a . The first contact surface 16a reaches the outer surface 12 of the housing 11 at its distal end 14.

The second electrode 17, which is annular and made of conductive material, extends along the central axis D around the first electrode 16. In particular, the second electrode 17 can be formed by the housing 11 itself, which in this case is made of conductive material. The second contact surface 17a of the second electrode 17 consists of a cylindrical section parallel to the central axis D and the corresponding side surface of the housing 11, and of an annular section transverse to the central axis D and the corresponding distal surface of the housing 11.

Between the first 16 and second 17 electrodes is a layer of electrical insulating material 15. A layer of electrical insulating material 15 extends along the housing 11 from the proximal end 13 of the housing 11 to the distal end 14 of the housing 11, to which it reaches the free end surface 15A. In the present embodiment, the annular layer of electrical insulating material 15 is located along the central axis D around the first electrode 16 and inside the second electrode 17.

The invention is not limited to the embodiment and arrangement of the housing 11, the first 16 and second 17 electrodes and the layer of electrically insulating material 15 described above. In general, the first 16 and second 17 electrodes are not necessarily coaxial. In particular, these first 16 and second 17 electrodes can each be made in the form of a rod of conductive material immersed in the housing 11. In addition, the first electrode 16 and the second electrode 17 can each have an insulated contact surface 16a, 17a, reaching the side surface or the distal surface of the housing 11. In addition, the housing 11 can serve to attach two or more of the first two electrodes 16 and two or more of the two second electrodes 17.

The handle 20, made in the form of a cylindrical body of revolution, is located essentially coaxial with the central axis D of the housing 11. The handle 20 has a shape that facilitates holding in the hand and manipulating the tool 10. The handle 20, made of plastic material, is fixedly connected to the sleeve 18 of plastic material located on part of the outer surface 12 of the housing 11.

The handle 20 contains a socket 21, configured to accommodate an electric generator 22 and a processing device 23, for example, located on the electronic board 25, inserted into the socket 21 through an opening made at the end of the handle 20 opposite the housing 11. The removable cover 26 allows you to close nest 21.

The electric generator 22 is configured to supply an electric current M between the first 16a and second 17a contact surfaces. In the particular embodiment shown in FIG. 3, but not limited to this option, the electric generator generates an electric current M in the form of voltage pulses of 1.2 V with a measurement frequency of 5 Hz. In this case, the electric current M has a measurement period corresponding to a measurement frequency of 200 ms. Alternatively, the electric current voltage can be any voltage below 2 V, preferably from 1 V to 2 V, in particular from 1.1 V to 1.5 V. The measurement frequency can be from 4 Hz to 20 Hz, while the measurement period ranges from 50 ms to 250 ms.

The processing device 23 is configured to determine an electrical characteristic representing the ability of the bone structure 3 to conduct an electric current M between the first contact surfaces 16a and 17a 17a. In particular, based on the voltage of the electric current M, the processing device 23 can measure the strength of the electric current M passing through the tissue between the first 16a and second 17a contact surfaces. Based on the known voltage and the measured electric current strength, the processing device 23 can determine an electrical characteristic, such as resistivity. This measurement of the electric current M and the determination of the specific resistance can be carried out in accordance with the frequency of measurement, and the measurement is carried out with each pulse of the electric current M. Alternatively, the electric generator 22 can generate an electric current M, the strength of which is known, and the processing device 23 can be configured to measure the voltage of the electric current to determine the electrical characteristic based on the known strength and the measured voltage of the electric ka.

The tissues of the bone structure 3 have different abilities to conduct electric current. For example, a cortical bone has a resistivity greater than that of the cancellous bone, which in turn has a resistivity greater than that of fluids such as blood. Such a processing device 23 makes it possible to comparatively detect a tissue change based on a change in resistivity and even absolutely identify a tissue based on a resistivity value.

The processing device 23 is also configured to issue a warning signal corresponding to a specific resistivity. The warning signal may be an audible warning signal, a light warning signal, a tactile warning signal (vibration), or a combination of such warning signals.

Shown in FIG. 2 A warning signal, such as a beep, is intermittent. It has a warning rate in accordance with which the doctor-detected warning portions Sa are sequentially transmitted at a time interval Si between two successive warning portions Sa. In particular, the warning rate may be from 1 Hz to 20 Hz. The warning rate characterizes the speed at which the warning sections Sa are transmitted, for example corresponding to short beeps in the case of an audible warning signal. In a particular embodiment of the invention, each warning portion Sa has the same duration, for example 35.5 ms, while the time interval Si corresponding to the silence time varies depending on the warning rate. A warning period corresponding to the warning rate and comprising the warning portion Sa and the time interval Si is also determined.

In addition, each warning portion Sa is periodic and has a warning frequency. In particular, the warning frequency can range from 470 Hz to 2600 Hz. The warning frequency characterizes the tonality of each of the warning sections Sa, while the warning section moves from low to high tonality with increasing warning frequency. In a particular embodiment of the invention, each warning section contains a series of pulses, each of which has the same duration, for example 230 μs.

Each warning portion Sa may also have a warning amplitude indicative of the intensity with which the warning portion Sa is transmitted.

In the embodiment shown in FIG. 3, the processing device 23 is configured to change all parameters of the warning signal, namely, the warning rate, the frequency of the warning, and the amplitude of the warning, depending on the resistivity. In particular, the processing device 23:

- increases the pace of the warning, the frequency of the warning and the amplitude of the warning of the warning signal when the resistivity decreases, and

- reduces the pace of the warning, the frequency of the warning, and the amplitude of the warning of the warning signal when the resistivity increases.

Alternatively, the processing device 23 is configured to determine electrical conductivity as an electrical characteristic and with the ability to:

- increase one or more parameters of the warning signal selected among the warning rate, warning frequency and warning amplitude when the conductivity increases,

- reduce one or more parameters of the warning signal selected among the warning rate, warning frequency and warning amplitude when the conductivity decreases.

In addition, as follows from the foregoing, only one or two of the parameters selected among the warning rate, warning frequency and amplitude of the warning can vary depending on a specific electrical characteristic.

Furthermore, as shown in FIG. 3, when a change in resistivity is detected, the processing device 23 changes the parameter or parameters of the warning signal only after the delay time T has expired. This delay time can be selected in any appropriate way to avoid disturbances in the warning signal. It can be fixed or variable.

As shown in FIG. 3, four measurements are taken sequentially in three different anatomical structures. After the first measurement, the first delay time T1 can be arbitrarily selected, in particular as part of the measurement period. For the following measurements, the delay times correspond to the unexpired parts of the warning period of the warning signal corresponding to the resistivity determined in the previous measurement.

Thus, during the penetration of the housing 11 into the first anatomical structure, a first warning signal A is issued. During the first measurement of M1, the processing device 23 determines the first resistivity. After an arbitrary first delay time T1, it generates a warning signal with the corresponding first warning pace, warning frequency and warning amplitude. In the second measurement M2, the processing device 23 determines a second resistivity less than the first resistivity. After the second delay time T2, essentially corresponding to the time interval of the warning signal of the first measurement, it issues a warning signal with a corresponding second warning pace, warning frequency and warning amplitude exceeding the first warning pace, warning frequency and warning amplitude. In the third measurement M3, the processing device 23 determines a third resistivity in excess of the first and second resistivities. After the third delay time T3, which corresponds to the part of the warning period containing the pulses of the warning section and the time interval of the warning signal of the second measurement, it gives out a warning signal with the corresponding third warning rate, warning frequency and warning amplitude lower than the first and second warning rates, warning frequencies and amplitudes warnings.

Similarly, during the penetration of the housing 11 into the second anatomical structure, a second warning signal B is issued. In a first measurement of M1, the processing device 23 determines the first resistivity. After an arbitrary first delay time T1, it generates a warning signal with the corresponding first warning pace, warning frequency and warning amplitude. In the second measurement M2, the processing device 23 determines a second resistivity less than the first resistivity. After the second delay time T2, which corresponds to the portion of the time interval of the warning signal of the first measurement, it issues a warning signal with the corresponding second warning pace, warning frequency and warning amplitude exceeding the first warning pace, warning frequency and warning amplitude. In a third measurement of M3, the processing device 23 determines a third resistivity less than the first resistivity and greater than the second resistivity. After the third delay time T3, essentially corresponding to the portion of the warning period containing the pulses of the warning portion and the time interval of the second measurement warning signal, it issues a warning signal with the corresponding third warning rate, warning frequency and warning amplitude exceeding the first warning rate, warning frequency and amplitude warnings and lower second warning rates, warning frequencies and warning amplitudes.

During the penetration of the housing 11 into the third anatomical structure, a third warning signal C is issued. During the first measurement of M1, the processing device 23 determines the first resistivity. After an arbitrary first delay time T1, it generates a warning signal with the corresponding first warning pace, warning frequency and warning amplitude. In the second measurement M2, the processing device 23 determines the second resistivity. However, this measurement occurs during the second delay time corresponding to a portion of the time interval of the first measurement. In this case, no warning signal corresponding to the second measurement is issued until the third measurement of M3 is carried out. In the third measurement M3, the processing device 23 determines a third resistivity less than the first resistivity. After the third delay time T3, which corresponds to the portion of the time interval of the first measurement, it gives out an alarm signal with the corresponding second warning pace, warning frequency and warning amplitude exceeding the first warning pace, warning frequency and warning amplitude.

Alternatively, the delay time T can be selected by any other appropriate way. In particular, the delay time can be from 30% to 100% of the Si time interval, in particular from 50% to 100% of the Si time interval and, for example, from 60% to 90% of the Si time interval.

According to another embodiment, the delay time may be equal to at least a portion of the measurement period, preferably it may be from 10% to 500% of the measurement period. In this other embodiment, if the delay time is two times the measurement period, the processing device can calculate the average electrical characteristic based on the electrical characteristics determined in each of the measurement periods that occurred during the delay time. In this case, the parameter or parameters of the warning signal can be modulated depending on the calculated average electrical characteristic. This allows you to limit the sensitivity of the surgical instrument 10 to local heterogeneities.

Next, with reference to FIG. 4-7, a description is given of the use of a surgical instrument 10 during an opening in one of the vertebral legs. The cortical bone has a resistivity in excess of the resistivity of the cancellous bone, and the cancellous bone has a resistivity in excess of the resistivity of the blood.

In FIG. 4 shows an example of a transient function recorded in the processing device 23 and relating the value of the warning rate, warning frequency and / or warning amplitude to each of the resistivity values. When the tissue with which the first contact surfaces 16a and second 17a come into contact changes, a change in resistivity occurs, which is expressed by a change in at least one of the parameters among the warning rate, warning frequency and / or warning amplitude.

The transition function is chosen so as to reduce the rate of warning, the frequency of the warning and / or the amplitude of the warning as the resistivity increases.

Thus, when the first 16a and second 17a contact surfaces of the surgical instrument 10 come into contact with blood or with soft tissues having a low resistivity, the warning signal has an increased warning rate, warning frequency and warning amplitude. When the first 16a and second 17a contact surfaces of the surgical instrument 10 come into contact with the cancellous bone, the specific resistance of which lies between the specific resistance of blood or soft tissues and the specific resistance of the cortical bone, the warning signal has an intermediate warning rate, warning frequency and warning amplitude. And when the first 16a and second 17a contact surfaces of the surgical instrument 10 come into contact with a cortical bone having a high resistivity, the warning signal has a low warning rate, warning frequency and / or amplitude of the warning.

The transition function is also chosen so as to change the warning rate, the frequency of the warning and / or the amplitude of the warning to a greater extent at lower resistivities than at higher resistivities.

Thus, the surgical instrument allows displaying with higher sensitivity changes in resistivity in situations that pose the greatest risk to the patient, that is, when the first 16a and second 17a contact surfaces of the surgical instrument 10 come into contact or are near blood or soft tissues.

As shown in FIG. 5, two first measurements M1, M2 are made when the distal end 14 of the surgical instrument body 11 with the first 16a and second 17a contact surfaces comes into contact with the outer layer of the cortical bone. After the first delay time T1 following the first measurement of M1, a first warning signal corresponding to the specific resistance of the cortical bone is issued, and continues to be transmitted after the second measurement of M2, while no change in resistivity is detected. In the third measurement M3, the distal end 14 of the body 11 of the surgical instrument 10 penetrated into the cancellous bone. After the second delay time T2 following the third measurement of M3, a second warning signal corresponding to the specific resistance of the cancellous bone is issued, and it continues to be output after the fourth measurement of M4, while no change in the resistivity is detected.

As shown in FIG. 6, in the fifth dimension M5, the distal end 14 of the body 11 of the surgical instrument 10 is located near the inner layer of the cortical bone surrounding the vertebral foramen. After the third delay time T3 following the fifth measurement of M5, a first warning signal corresponding to the specific resistance of the cortical bone is issued, and it continues to be output after the sixth measurement of M6, and no change in resistivity is detected. In the seventh dimension M7, the distal end 14 of the body 11 of the surgical instrument 10 pierced the cortical bone, and blood enters the cavity formed by the body 11. After the fourth delay time T4 following the seventh dimension M7, a third warning signal corresponding to the specific resistance of the blood is issued, and continue to issue it after the eighth measurement of M8, while not detecting any change in resistivity.

As shown in FIG. 7, before the ninth measurement of M9, the doctor corrected the trajectory after receiving the third warning signal. The distal end 14 of the casing 11 of the surgical instrument 10 was returned to the spongy bone, and after the fifth delay time T5 following the ninth measurement M9, a second warning signal corresponding to the specific resistance of the spongy bone was issued and continued to issue it after the tenth M10, eleventh M11 and twelfth M12 measurements, while not detecting any change in resistivity.

Alternatively, in order to limit the sensitivity of the surgical instrument to local heterogeneities, ranges of resistivity can be determined based on thresholds. For each resistivity range, the appropriate alarm parameters can be selected. In this case, the parameter or parameters of the warning signal remain constant as long as a specific resistivity remains in a certain range, less than a certain threshold. When a specific resistivity changes the range of resistivity and goes over the corresponding threshold, one or more parameters selected among the warning rate, warning frequency and warning amplitude can change.

In particular, when using a surgical instrument similar to the surgical instrument described above, which allows determining the absolute value of the resistivity instead of simply changing this resistivity, three ranges of resistivity can be determined. So, you can determine:

- a first range of resistivity for the cortical bone, with which the first warning signal is associated with a low and constant warning rate, warning frequency and warning amplitude,

- a second range of resistivity for the cortical bone, with which a second warning signal is associated with an intermediate and constant warning rate, warning frequency and warning amplitude,

- the third range of resistivity for the cortical bone, with which the third warning signal is associated with a high and constant warning pace, warning frequency and warning amplitude.

Claims (24)

1. The medical system (10), designed to penetrate into the anatomical structure (2, 3) of the patient, and the anatomical structure (2, 3) contains tissues with different abilities to conduct electric current, while the medical system (10) contains: - a housing (11) configured to penetrate the anatomical structure (2, 3), the housing (11) having an outer surface (12), - at least one first electrode (16) containing a first contact surface (16a) located on the outer surface (12) of the housing (11), for coming into contact with tissues of the anatomical structure (2, 3), - at least one second electrode (17) containing a second contact surface (17a) located on the outer surface (12) of the housing (11) to come into contact with tissues of the anatomical structure (2, 3) at a distance from the first contact surface (16a), - an electric generator (22) configured to supply an electric current (M) between the first (16a) and second (17a) contact surfaces, - a processing device (23), configured to determine an electrical characteristic that displays the ability of the tissue of the anatomical structure (2, 3) to conduct electric current (M) between the first (16a) and second (17a) contact surfaces, and with the ability to issue a warning signal, corresponding to a specific electrical characteristic, the warning signal having at least one parameter varying depending on the specific electrical characteristic, wherein the warning signal is intermittent and has a warning rate at which the warning portions (Sa) received by the user are transmitted sequentially with a time interval (Si) between two successive warning portions (Sa), characterized in that the processing device (23) is configured to detect a change in the electrical characteristic and change the specified at least one variable parameter of the warning signal after the expiration of the delay time (T) following the change in the electrical characteristic. 2. The medical system (10) according to claim 1, wherein the delay time (T) is equal to at least a portion of the warning period corresponding to the warning rate, in particular equal to at least a portion of the time interval (Si), preferably from 30% to 100% of the time interval (Si), in particular from 50% to 100%, for example from 60% to 90%. 3. The medical system (10) according to claim 1, wherein the processing device (23) determines the electrical characteristic with a measurement frequency, wherein the electric current (M) has a measurement period corresponding to the measurement frequency, wherein the delay time (T) is at least as part of the measurement period, it is preferably 10% to 500% of the measurement period. 4. The medical system (10) according to claim 3, in which the delay time (T) is twice the measurement period, while the processing device (23) is configured to calculate the average electrical characteristic based on electrical characteristics determined in each of the periods measurements occurring during the delay time (T), and with the possibility of changing the parameter of the warning signal depending on the calculated average electrical characteristics. 5. The medical system (10) according to claim 3 or 4, in which the measurement period is from 50 ms to 250 ms, preferably 200 ms. 6. The medical system (10) according to any one of paragraphs. 1-5, in which the specified at least one variable parameter of the warning signal includes a warning rate, while the processing device (23) is configured to change the warning rate after the expiration of the delay time (T). 7. The medical system (10) according to any one of paragraphs. 1-6, in which the warning rate is from 1 Hz to 20 Hz. 8. The medical system (10) according to any one of paragraphs. 1-7, wherein said at least one variable parameter of the warning signal includes a warning frequency at which each of the warning sections is transmitted, wherein the processing device (23) is configured to change the warning frequency after the delay time (T) has elapsed. 9. The medical system (10) according to claim 8, in which the warning frequency is from 470 Hz to 2600 Hz. 10. The medical system (10) according to any one of paragraphs. 1-9, in which the specified at least one variable parameter of the warning signal includes the amplitude of the warning, the device (23) processing is configured to change the amplitude of the warning after the expiration of the delay time (T). 11. The medical system (10) according to any one of paragraphs. 1-10, in which the processing device (23) is configured to determine electrical conductivity as an electrical characteristic and with the possibility of: - increase the parameter of the warning signal when the conductivity increases, - reduce the alarm parameter when the conductivity decreases. 12. The medical system (10) according to any one of paragraphs. 1-10, in which the processing device (23) is configured to determine resistivity as an electrical characteristic and with the possibility of: - increase the parameter of the warning signal when the resistivity decreases, - decrease the alarm parameter when the resistivity increases. 13. The medical system (10) according to any one of paragraphs. 1-12, in which the processing device (23) is configured to keep the at least one variable alarm parameter constant while the electrical characteristic remains below a threshold and to change the warning parameter when the electrical characteristic reaches a threshold.

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